The packaging or coating of various chemicals is desirable, such that the handling or direct exposure to or of the chemicals may be reduced. Where the ultimate usage of the chemical is in an aqueous system, the use of a water-soluble packaging or coating may further reduce the handling and exposure to the chemical. Unfortunately, many water-soluble polymers are reactive to oxidizing chemicals, affecting the water solubility of the polymer, the color of the polymer, and the physical properties of the polymer, such as flexibility, as the polymer remains in contact with the oxidizing chemical during storage. Insolubility, color, and brittleness occur during storage due to reaction of water soluble polymers with the oxidizing chemical being packaged.
One example of water soluble films used as a packaging material is polyvinyl alcohol (PVOH). PVOH films, for example, are commonly used as a delivery system for chemicals having relatively low reactivity or oxidizing properties, i.e. non-aggressive oxidizing chemicals, such as certain laundry or dish detergents, as the films exhibit good strength, impact resistance, and are soluble in water.
The solubility of PVOH films, however, rapidly decreases when exposed to certain chemicals, such as oxidizing chemicals, acid chemicals, alkali chemicals, chlorine-containing substances, salts with polyvalent metals, boric acid, polyamines, insecticides, and herbicides, among others. Thus, in applications which employ these types of chemicals, the use of PVOH packaging is restricted, as the effective shelf-life of the unit dose products is limited by their solubility in water.
Modified PVOH films, having co-monomers and/or various additives, have been shown to improve the chemical resistance of the films. For example, see U.S. Pat. Nos. 6,608,121, 6,166,117, 6,787,512, 6,821,590, 7,005,168,and 7,745,517, among others, disclosing use of various plasticizers, additives, and co-monomers such as N-vinylamide, carboxyl and carboxylate functional groups, and sulfonic acid functional groups.
U.S. Pat. No. 5,102,950 discloses a PVOH film formed from a copolymer consisting of vinyl alcohol units, vinyl ester units, and copolymerization units containing a 2-pyrrolidone ring. Other comonomers are also contemplated, including sulfonic acid groups, quaternary ammonium structures, and others. For use in unit-dose packaging films, it is disclosed to use plasticizers such as a polyhydric alcohol and linear sugar alcohols having 4 to 6 carbon atoms.
U.S. Pat. No. 6,956,070 and EP1251147 disclose that films containing a 2-pyrrolidone ring have a problem of insufficient cold water solubility. Instead, it is disclosed that it is possible to provide a water-soluble film simultaneously satisfying the requirements in regard to water solubility, biodegradability, and physical properties when the PVOH is modified with monomers including an N-vinylamide, a carboxyl group and lactone ring.
U.S. Pat. No. 6,166,117 discloses a water-soluble film including a sulfonic acid group modified polyvinyl alcohol in admixture with gallic acid. In this patent, it is noted that 2-acrylamido-2-methylpropanesulfonate-modified polyvinyl alcohols are unsuitable for storage of acidic chemicals for long periods of time, as they lose their function as a water-soluble film. The gallic acid is taught as necessary to achieve the desired properties.
As can be seen by the brief background above, there has been a large focus on the use of comonomers to enhance the viability of water-soluble polymers as a packaging material for oxidizing chemicals. Unfortunately, many of these efforts have not resulted in a water soluble polymer that solves the problem of water insolubility, color formation, and brittleness.